1. Field of the Invention
The present invention relates to a method, which uses corpuscular beams, and for which the positioning of the corpuscular beams is necessary, such as testing with corpuscular beams. Particularly, the present invention relates to methods for calibrating the beam position and means qualified therefore. Specifically, the present invention relates to a method for calibration of the beam position of the corpuscular beam of a testing device and the usage of a product for calibration of the beam position.
On increasing demand for display elements without a cathode ray tube, the requirements increase for liquid crystal displays (LCD) and other display elements, for which control elements such as thin-film transistors (TFT) are used. For those display elements, the picture elements, so-called pixels, are arranged in an array.
2. Description of the Related Art
In order to assure a good picture quality of the display elements, only very few of the for example several million pixels may be defective. In order to provide an inexpensive production, it is, thus, especially for the display elements steadily increasing in size, important to provide effective in-line test methods. Such a test method is for example disclosed in publication EP 0523584. For these test methods, the individual picture elements are tested with a corpuscular beam. The corpuscular beam can either be used to detect charge applied via the supply lines and/or it can be used to apply charge on a pixel electrode.
For the test methods of the individual picture elements, it is inter alia necessary to scan or to address the picture elements with the corpuscular beam. That is, the corpuscular beam is to be guided on individual picture elements. In case of charged particles as corpuscles, this deflection may be carried out by magnetic, electrostatic or magneto-electrostatic deflectors. In case of photons as corpuscles, the deflection may be carried out by mirrors or other suitable means.
The necessary control of the deflectors depends on the geometrical arrangement and on the characteristic of the electronic, and is without calibration not exactly known because of the tolerances. Further, the correlation between the control current or the deflection voltage and the deflection of the corpuscular beams is not linear. A calibration of the beam position is necessary, so that the deflector can be controlled accordingly during a test method. The intention of the calibration is to assign to each coordinate x,y in a substrate plane, a beam coordinate in the control processor (x*,y*) or the values thereof (x**,y**), that is currents or voltages, for the control.
Such a calibration is particularly necessary for the test of LCD displays with an electron beam, for which the beam needs to be positioned on the pixels of the display. However, calibration may also be necessary for other methods, which irradiate the substrate with a corpuscular beam, such as a laser beam, a light beam, an ion beam, or an electron beam for testing or processing.
According to the prior art, for the calibration of the beam position, a pattern sample especially produced therefore is fabricated, which provides certain features at predetermined positions. In case of LCD displays, coated glass plates are provided, which have so-called L-features in larger regular distances. The positions of the features are known. If the calibration plate is scanned with for example an image forming electron microscope, it is possible to the position of the L.-features. The known positions of the detected features may be related to the signals in the control processor. Thereby, a calibration of the beam position of the corpuscular beam is possible.
As a result of the displays increasing in size, it becomes increasingly difficult and expensive to fabricate suitable calibration substrates. Further, these specific substrates need to be stored and need, if required, to be introduced in the apparatus to calibrate the beam positions.